Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SYSTEM AND METHOD FOR HEAT CONTROL
OF A LIVING BODY
FIELD OF THE INVENTION
The present invention concerns a systeln and method for
thermoregulations of a living body. The system and method of the invention
may be applied to both humans and animals.
BACKGROUND OF THE INVENTION AND PRIOR ART
A living body can maintain a normal body temperature, which in
humans is about 36.5-37 C, under normal conditions. However, when
subjected to extreme temperature conditions or to a variety of medical
treatments, the body may not be able to properly regulate the body
la temperature. This is the case, for example: in individuals exposed to
extreme
temperatures; and in a variety of physiological disorders and medical
conditions (e.g. general anesthesia) where the body loses its ability to
properly
regulate the body temperature.
Hypothermia is a reduction in body temperature which may result from
exposure to a cold enviromnent. Mild hypothermia in which body's core
temperature (namely the temperature of internal organs and tissue within the
body) is reduced by about 2 C below the nonnal temperature, commonly
occurs during and following surgery that is conducted under general
anesthesia, as patients tend to lose body heat due to lowered metabolism and
2o as a result of exposure of internal body organs or tissue, e.g. in an
abdominal
or thoracic cavity, to ambient air.
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Hypothermia is experienced by more than 60% of patients after
surgery, and in some surgical procedures, e.g. open heart surgery, hypothermia
is experienced by more than 90% of adult patients.
Hypothermia can cause various severe pliysiological problems
s including cardiac morbidity, coagulopathy, impaired immune function,
iinpaired wound healing, shivering, altered pharmaconnected properties of
drugs, etc.
Hyperthermia, namely increase in body teinperature above normal
levels, may also cause various physiological disorders and if extreine, may be
1 o life threatening.
The clinical need to provide means for body temperature control has
long been recognized.
MicroClimate Systems Inc., Stanford, MI, U.S.A., markets a series of
portable personal cooling systems (sold under the trademarks KOOLVEST,
15 KOOLJACKET, KOOLBAND, KOOLPAID and others) which are
intended for use by healthy persons who perform a physical activity in a hot
environment (see Internet http://wwvc!microclimate.com/T)rodline.html or
http:/hwww.microclimate.com/work.htrnl). The system consists of a gannent
(it may be a vest, jacket, skull cap, a cervical collar, etc.) with tubing
2o einbedded therein in which water flows propelled by a battery-powered pump.
Water passes through ice or through a cooling device before entering the
tubing within the garment. The user can control the pump rate, the
teinperature, etc. A similar product line is also provided by Mallinckrodt
Inc.,
St. Louis, MO, U.S.A. (see the Internet at http://www/hnallinckrodt.com/ccd)
25 and others.
A similar system is disclosed in U.S. Patent 4,807,447 (Macdonald
et al. ). The unique feature of this system is that the person's breathing is
used
to operate the refrigerant compressor.
Various systems making use of gannents, pads or blankets with heat
;o transfer elements, e.g. conduits embedded therein, are disclosed in U.S.
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Patents 3,738,367, 4,094,357, 4,094,367, 4,149,541, 4,843,072, 5,154,512,
4,691,762, 5,269,369, 5,6 09,619 and in W096/26693. However, due to various
physiological reasons, realized only in accordance with the preseb.t invention
and
which wil] be specified fiuther below, none of the above systems provides
adequate
control of body temperature of the individuals in general, and of patients
following
surgery before undertaking general anaesthesia in parti,cular.
There is also a need for control of body temperature in veterinary medicine,
particularly the control of body ternperature during surgery under general
anaesthesia. Animals, and particularly small animals , oceasionally die
following
surgery, owing to uncontrolled changes in body temperature.
GENERAL DESCRIPTION OF THE IN"VENTION
In the following, the term "core temperature" will be used to denote the
temperature within the body, namely that of the internal organs aud tissue.
Core
temperature is typically measured through the rectum ("rectal temperature
measurement) but znay also be measuTed by inserting probes through a variety
of
other body cavities, e.g. mouth, nasal or ear temperature probes. The tern
"surface
temperature" will be used to denote the temperature of the external body
suxface,
(which may be that of the aldn or, where the sldn bas been removed, e.g. in a
burn
injury, that of the most external layers). It sbould be noted that surface
temperature
may vary between different body portions. The surface temperature may be
measured
by a variety of temperature probes including, for example, an infrared sensor
measuring infrared emission from a specific skin portion, probes attached to
the skin
such as a thermo-couple devices, thernnistor, etc.
In accordance with the pi-esent invention, it has been realized that a major
deficiency of prior art the.rnaoregulatory devices is that these do not
sufficiently
reconcile the fact that the body is not a passive heat conductor but rather
employs
intrinsic dynamie physiological thermoregulation meehanisnis which can change
the
heat transfer properties between the body's core and the
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periphery. For example, when exposed to a low temperature, there is a
vasoconstriction of peripheral blood vessels, thus reducing blood flow to the
periphery and thereby reducing heat transfer between the periphery and the
body's core. In other situations there is vasodilatation resulting in
increased
s blood flow to the periphery above normal levels thus bringing an increase in
heat transfer rate between the body's core and the periphery.
In accordance with the invention, a system and method for the control
of body temperature is provided. The system and method of the invention
allows controlled cooling of body temperature, controlled heating, as well as
i o regulating an individual's body temperature to remain at a desired set
temperature. It is a unique feature of the invention that it takes into
consideration the coinplexity of the heat transfer regiment from the skin to
the
body's core. This complexity is manifested by dynamic heat transfer
properties, namely physiological changes which can alter the rate in which
15 heat can be transferred between the skin and the body's core. Such heat
transfer dynamics (HTD) may be determined by a variety of means, as will be
illustrated further below.
In accordance with the invention there is provided a systein for
controlling an individual's body core temperature (BCT) comprising:
20 - a heat exchanger for transferring heat to or removing heat from
portions of the individual's body surface;
- at least one BCT-sensing device for measuring the individual's
actual BCT (aBCT) and emitting an aBCT data signal;
- at least one sensing device for measuring a parameter indicative
25 of the heat transfer dynamics (HTD) between the body surface and the body's
core, and emitting an HTD data signal; and
- a control module for receiving data signals from measuring
devices, comprising the aBCT data signal and the HTD data signal, and for
emitting a control signal for controlling heat exchange properties of said
heat
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exchanger as a function of the data signals and the desired body core
teinperature (dBCT).
The heat exchange may either be provided with an intemal heat or cold
producing capability, e.g. including a Peltier effects modules, or the heat
s exchanger may be linked to at least one source of cold and/or hot fluid,
which
fluid then circulates between such source and the heat exchanges to transfer
heat/cold between the exchanger and said source.
By another aspect, the present invention provides a method for
controlling internal body temperature of an individual, comprising the
io following steps:
(a) defining a desired body core teinperature (dBCT);
(b) providing a heat exchanger and bringing it into contact with at
least a portion of the individual's external body surface, for heat transfer
to or
heat removal from the body portion;
ls (c) continuously measuring parameters including at least the actual
body core temperature (aBCT) and a parameter indicative of the heat transfer
dyna.inics (HTD) between the body's surface and the body' core; and
(d) in a processor, receiving data signals corresponding with the
measured parameters, comparing the aBCT with the dBCT, defming based
20 thereon whether there is a need for heating or cooling and emitting a
control
signal controlling heat transfer properties of said heat exchanger based on
the
aBCT/dBCT difference and on said HTD.
The control of the heat exchange properties of said heat exchanger
may involve change of the heat transfer properties between the heat
25 exchanger and the body surface which may be achieved, for exainple, by
changing the heat conductance parameters between the body's surface and the
slcin, e.g. by pumping or removing air into or from air pockets disposed
between heat radiating/heat absorbing members within the heat exchanger
and the slcin; or preferably, by changing the teinperature of the heat
3o exchanger, which may either be a reduction in the extent of heating or
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cooling, halting the heating or cooling operation, or reversing the heating or
cooling operation into cooling or heating, respectively. In reversing, the
heat
exchanger acting first as a heat source will be switched to become a heat
sink,
or vice versa, thus reversing the direction of heat transfer.
The heat exchanger may, for example, comprise electric heating/
cooling devices, e.g. Peltier devices and others. However, in accordance with
a preferred, non-limiting, embodiment of the invention, the heat exchanger is
of a kind comprising one or more conduits or fluid transfer medium for
passing the heat control fluid therethrough, for transferring heat to or
I o absorbing heat from the individual's body surface. The fluid, which is
typically, though not exclusively, a liquid, e.g. water, may be driven through
the conduits or medium by a pump or any other suitable device therefor. Such
fluid thus circulates between the heat exchanger and a heat and/or cold
source. The heat exchanger is typically flexible to allow it intimate contact
with a body surface for efficient heat transfer therewith.
In addition to the above noted measuring devices (the BCT sensing
device and the device for measuring a pararneter indicative of said HTD), the
system may further coinprise one or more devices for measuring temperature
of the circulating fluid and for emitting data signal relating thereto to the
controller. At times, where the system coinprises two or more such devices, at
least one of which may serve as an inlet teinperature sensing device for
measuring temperature of the fluid as it enters the at least one conduit or
fluid
transfer medium, and at least one other may serve as an outlet temperature
sensing device for measuring temperature of the fluid as it exits the at least
one conduit or fluid transfer medium. The temperature drop (AT) between the
garment's inlet and the outlet is a very good indicator of said HTD, since
this
information, together with information on the fluid's flow rate, permits an
accurate calculation of the heat transfer between the heat exchanger and the
body, which depends on said HTD. Thus, in accordance with a preferred
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embod'unent said OT and the fluid flowrate are used as an HTD-indicating
parameter.
The heat exchanger of the invention is typically a garment which is
worn over a portion of the individual's body. Typically, the garment may be
designed so as to cover at least about 30%, preferably at least about 40% of
the body's surface. In this way, the system of the invention effectively
stabilizes an individual's body temperature, at a desired body core
temperature, within a minimal tolerance. Such a gannent may have different
forms depending on its intended use. For example, the gannent may be
i o designed for use by individuals performing hard labor under extreme hot
conditions, for the purpose of cooling their body. For such a purpose the
gannent has to be relatively flexible so as to limit, as little as possible,
the free
movement of the individual. By another example, the gannent may be
designed for medical use, either for the purpose of reducing core teinperature
of individuals having a disease with a very high fever, for the purpose of
increasing core body temperature of hypothermic individuals or for both. A
currently preferred embodiment of the invention is the application of the
system for control of body temperature of patients during or after general
anesthesia. For this purpose the heat exchanger, typically in the form of a
garment, may have a variety of openings permitting access for the
perfonnance of various surgical procedures, for parental administration of
drugs or fluids or for drainage of body fluids, (e.g. excretions or blood).
One example of the use of the system and method of the invention in
accordance with the above referred embodiment, is in open heart surgery.
Open heart surgery typically involves cooling of the body temperature to
about 32 C. During such surgery the heart's activity is temporarily arrested
and the blood is circulated through an artificial heart-lung apparatus.
Following such surgery, there is a need to increase the body teinperature to
nonnal teinperature as rapidly as possible, since maintaining such a core body
telnperature for prolonged time periods may be dainaging, at times even life
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threatening. Today's medical practice involves, towards the end of the
surgery, heating of the blood as it circulates through the artificial heart-
lung
apparatus. However, this heating practice has proven insufficient, as the
body's core is not sufficiently heated in this way, and once the blood is
disconnected from this apparatus and allowed to recirculate through the
reactivated heart, the blood temperature immediately drops. Heating in such
procedures is typically performed today by the use of heated blankets,
blowing of hot air on the individual, etc. Overall, the methods available
today
do not allow an efficient monitoring and control of body core temperature. In
to accordance with the invention, the body core teinperature may be
controllably
cooled during the initial phases of the surgery, then maintained at about 32 C
while applying heating or cooling as needed, and then eventually controllably
heated at the end of the surgery to reach normal body teinperature.
Generally, the system and method of the invention may be used in
control of patient's body temperature during the perioperative period in a
wide range of different surgeries.
As will no doubt be appreciated, a heat exchanger in the form of a
gannent may typically be designed to have various forms and sizes, to meet
specifications of individuals of various ages, weights, agendas, etc., or to
meet specific requirements of a specific medical procedure.
In addition to use for humans, particularly in human medicine, the
method and system of the invention may also find a wide range of
applications in veterinary medicine. The saine problems of resuming normal
body temperature, as well as a controlled cooling during surgery, are also
encountered in veterinary medicine. As will be appreciated, the heat
exchanger, typically in the form of a pad, a blanket or garment, may be
designed to have different shapes, depending on the type of animal, the type
of surgery, etc.
A system of the invention for use in the operation room, may typically
;o be designed for exchange of data with other instruments present in the
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operation room, e.g. import of data relating to blood temperature from
heart-lung apparatus, iinport of data relating to heartbeat or blood pressure
from respective measuring devices, etc.
The sensing device for measuring a skin parameter indicative of said
s HTD (hereinafter referred to at times as "HTD device "), may, in accordance
with the one embodiment, include a device for measuring a temperature at a
skin portion proximal to a skin portion on which the heat exchanger is
applied. The HTD may then be determined, for exainple, by either one or both
of
(i) determining the rate of temperature change at said skin portion
following heating or cooling of adjacent skin portions by the heat exchanger,
or
(ii) by assessing the rate of change of temperature difference
between the skin portion and the core during heating or cooling of the body.
Said HTD device may, in accordance with another embodiment of the
invention, consist of the aforementioned at least two sensing devices for
measuring temperature of the fluid as it enters the at least one conduit in
the
heat exchanger and the temperature as it exits from the at least one conduit.
The controller, thus receiving at least two data signals relating to the
measured temperature, then calculates said HTD based on the inlets or outlet
teinperature differential and on the fluid flow rate, which is either
determined
by the controls or measured by an appropriate ineasuring device.
In accordance with other elnbodiments, said HTD device is adapted for
measuring a parameter indicative of said HTD, which paraineter may be one
of a variety of skin and peripheral blood flow parameters. These may be
detennined by many techniques, e.g. by echo doppler signal techniques, skin
conductance, peripheral blood pressure, skin temperature, slcin color, etc.
One major feature of the invention relates to the measurements of said
heat transfer dynamics (HTD), and taking the heat transfer dynamics into
consideration in the heat control regime of the individual. Specifically, when
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the HTD parameters point to the occurrence of vasoconstriction, any applied
cooling should be temporarily halted or reduced. At times, it is advantageous
also to reverse the heat transfer mode, temporarily heat in a cooling mode.
This means that a cooling mode will involve occasional heat pulses timed and
s patterned according to said HTD.
The system may have a user interface pennitting a user to enter a
dBCT, namely a temperature set point of the systein. The user interface may
further comprise control means allowing selective operation of the system in
either an autoinatic mode, namely in a mode pennitting both cooling or
lo heating depending on the direction or deviation of the aBCT from the dBCT.
In addition, the control means may also typically allow to select a heat only
mode or a cool only mode.
Typically, the heating will be limited so that the teinperature at the
surface of the heat exchanger which is in touch with the body surface, will
not
15 exceed maximum temperature, e.g. a temperature of about 40 C and not to
fall below a miniunuin temperature, e.g. about 15 C.
In order to be effective in cooling or heating, the heat exchanger,
typically in the form of a gannent, has to be fitted onto the individual's
skin.
At times, there is a need to wear such a garment for a prolonged period of
20 time, and this may give rise to a risk of pressure wounds. In order to
circurnvent this problem in accordance with one embodiment of the
invention, the heat exchanger has two or more individually flow-controlled
flow sub-systems, and these sub-systems may then be used intennittently,
namely, one system being inflated with fluid and used, while the other being
25 deflated and thus not exerting pressure on the skin; and vice versa. In
accordance with another embodiment, the fluid transfer to the gannent is
temporarily halted for periods of several seconds to minutes in order to
reduce
the pressure onto the skin thus reducing currents of pressure.
In accordance with one embodiment of the invention, the system
;o comprises an electric in-line fluid heating/cooling unit and the
circulation
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fluid is directed to flow through said unit for heating or cooling. Heating or
cooling of the fluid in such a unit may also be achieved by means of an
auxiliary circulatory heat transfer fluid through the intermediary of a heat
exchanger within said unit. In accordance with ailother embodiment, the
system comprises at least one cold fluid reservoir and at least one hot fluid
reservoir and comprises a fluid flow control system for selectably drawing
fluid from these reservoirs. One advantage of having independent hot and
cold fluid reservoirs, is that the switching between heating and cooling modes
can be rapid.
In a system comprising independent hot fluid and cold fluid reservoirs,
the flow control system is preferably adapted to permit return fluid to flow
back into the reservoir from which it was drawn. lt is preferred that during
switching from a cold to hot fluid or vice versa, the original fluid will flow
initially to the reservoir from which it was drawn, and only after the warm
fluid has been exploited will the returned fluid be directed to the other
reservoir. Otherwise, the cold reservoir may be heated or the hot reservoir
cooled. This may be achieved by having a temperature sensing device
measuring the temperature of the fluid flowing out of the heat exchanger and
only when the device measures an abrupt teinperature change, will the flow
control systein begin to direct the fluid to the new reseivoir.
In order to understand the invention and to see how it may be carried
out in practice, a preferred embodiment will now be described by way of a
non-limiting example only, with occasional reference to the annexed
drawings:
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BRIEF DESCRIPTION OF THE DRAWINGS
Fig. lA is a garment in accordance with an embodiment of the
invention.
Fig. 1B is an enlargement of the region marked "B" in Fig. lA with
the two external layers being partially separated for illustrative purposes.
Fig. 2 illustrates a top view of a laid-open garment, for use in the
system in accordance with an embodiment of the invention.
Fig. 3 is a schematic illustration of the garment of Fig. 1, applied to a
patient.
Fig. 4 is a side elevation of the patient with the garment of Fig. 3.
Fig. 5 shows a garment in accordance with another embodiment of the
invention, in an open state with the patient lying thereon provided with an
adhesive matrix.
Fig. 6 is a schematic general illustration of a system in accordance
with the invention.
Fig. 7 is a schematic side elevation of the system of Fig. 6.
Fig. 8 is a principal schematic illustration of a system in accordance
with another embodiment of the invention.
Figs. 9A and 9B show a schematic block diagrain of the algorithm
operating in the system in accordance with one embodiment of the invention.
(Fig 9B is continuum of Fig. 9A).
DETAILED DESCRiPTION OF PREFERRED EMBODIMENTS
A top view of a garment 2 in accordance with one embodiment of the
invention shown in an open layout can be seen in Fig. 1. Garment 2 is
designed for fitting over a person's torso. Garment 2, as can specifically be
seen in Fig. 1B, is formed with two external layers 4 and 6 defming between
thein a fluid passage space 7. The garment is provided with a fluid inlet 8
and
a fluid outlet 10 for respective fluid ingress and egress into and out of the
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fluid passage space. The garment is provided with a partition 12 which
defines a fluid flow-path which is represented sclieinatically by arrowed
line 14. This fluid is typically water but may also be any other suitable
liquid,
e.g. alcohol, oil, etc., and may also, in other embodiments be a gas, e.g.
air.
As can further be seen in Fig. IB, the garment is formed with a matrix
of welded points 16 where the two external layers 4 and 6 of the garment 2
are welded one to another. In use the pressure of the fluid forces the two
layers away from one another filling fluid in the space between the welded
points. The welded points ensure the structural integrity of the two layers
and
further ensure some resistance to fluid flow and consequently substantially
even distribution of fluid flow through the garment's entire fluid passage
space 7. As will no doubt be appreciated, the internal structure of the
garment
is but an example. By other embodiments the gannent may comprise two
external layers sandwiching a porous matrix between them; may comprise
tubes or other conduits embedded or defined therein by welded lines; etc.
A top view of a garment in accordance with another embodiment
shown in open layout, and generally designated 20, can be seen in Fig. 2. The
gannent 20 has openings 22 and 24, which allow, when the garment is fitted
on a person, access to the underlying skin portion, e.g. for skin temperature
measurements, for injection, etc. Rather than openings 22 and 24 the garment
may also be provided with flaps serving a silnilar purpose. The garment is
provided with several cuts 28, 30 and 32 for fitting of the garment on the
individual, as can be seen in Fig. 3. The garment which may have a similar
internal structure to that shown in Fig. 1B, is formed with weld lines 34A,
34B, 35, 36A and 36B which together define a fluid flow path as represented
by arrowed lines 37A, 37B, 37C and 37D extending between the fluid inlet
44 and outlet 46. In this case, the garment is structured such that the chest
and
abdoininal portion of the individual are left open, thus rendering this
garment
suitable for chest and abdominal surgery. For other surgical applications, the
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gaxment may assnme a variety of different shapes. In addition, the garment may
also
be provided in various sizes for fitting individuals of different weights,
gender, age,
etc.
The garmment may be made of a variety of different materials including
fabrics, plastic materials, etc. The garment should preferably be ilexible and
elastic to
allow it to fit over an iz+dividual's body. The outer layer of the fabric may
be coated
with a heat insulating material, to prevent heat transfer to the external
environment. In
addition, the garment may have an internal soft Iining such as felt, in order
to avoid
occUlCrenee of pressure wounds.
Furthermore, as will be explained with reference to Fig_ 5, the garment may
be provided with an internal fluid absorbent layer.
The garment may be made for multiple use, or occasionally may be made
disposable. The gatment made for multiple use should be made of such materials
as to
allow its sterilization by any one of a plurality of sterilization means lmown
per se.
As can be seen in Figs. 2-4, fluid inlet/outlet tubings 44, 46 are eonnectable
to
a liquid temperature contirol unit 48 (seen in Fig. 4).
In order to allow easy fixing and removal of the garment, it is typically
provided with detachable fixing rneans, such as a hook and pile (e.g.
VelcroTM) type
attachment members 49.
Fig. 5 is a planar view of a garment 120 in accordance with another
embodiment of the invention, still in an open position, prior to fixing it
over the
patient's body. In this figure, like reference numerals to those of Figs. 2-4
were used,
with a "100" index (namely with a"1 " prefix) and the reader is referred to
the
description relating to Figs. 2-4 for their explanation. Further seen in Fig.
5, are
matrices 50 which are made of an absorben.t material. 7ypically, sueb a matrix
lias a
fluid pertneable layer, and a bygroscopic material capable of absorbing
liquids and
retaining them within. Such matrices of liquid absorbent properties, are
readily known
in the art, and a detailed description of their structure goes beyQnd the
present writing.
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Also seen in Fig. 5, are skin-temperature sensing probes 60 and 62 and
a rectal temperature probe 64 for measuring core temperature. In addition,
other types of temperature measuring devices may be provided, e.g. an
intra-ear temperature measuring device, an infrared sensor for measuring skin
temperature, an oral temperature measuring device for measuring core
telnperature, etc. As explained above, the slcin temperature is measured, in
accordance with one embodiment of the invention, in order to determine the
heat transfer dynamics (HTD) of the skin. For the same purpose, as an
alternative to measurement of skin temperature, other parameters may be
i o measured which include skin color, skin conductance, peripheral blood
pressure, temperature drop of the heating or cooling fluid (as will also be
outlined below), as well as any other paralneters which can give an indication
of occurrence of vasoconstriction or vasodilatation.
In addition, advantageously, temperature sensing devices 70 and 72 for
measuring inlet and outlet fluid temperature may also be provided. Such
information may also be utilized for the rate of heat transfer between the
heat
exchanger, namely the garment, and the skin in order to assess the HTD.
A schematic representation of the system in accordance with another
embodiment of the invention can be seen in Figs. 6 and 7. A patient 80 as
shown herein is provided with a garment 220 (shown schematically as a
rectangle in Fig. 5). In Figs. 6 and 7, the saine reference numerals to those
used before are used, where applicable, with "200" index. Garment 220 is
provided with a fluid inlet 244 and outlet 246 and with a continuous fluid
conduit or a continuous porous space 240 between them, embedded in
gannent 220. A plurality of sensing devices shown herein schematically as
component 90, transmit data signals reflecting the patient's physiological
paraineters, are transmitted to controller 94.
The system of this embodiment is adapted for both heating or cooling
the patient. By one embodiment, hot fluid and cold fluid are provided from
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respective, independent hot and cold fluid reservoirs 96 an.d 98. Each of the
reservoirs has respcctive fluid inlets 101, 102 ana respective fluid outlets
143,
104. Tbe system is provided with a pump 105 foc propelling fluid wi#lain the
:ystem.
$ The system is provided with two flow control valves 106 and 107, for
selectively transferring retUm fluid to or dra7Aing fluid from one of the two
reservoirs. Pump 105 and flow control valves 106 and 107, are electrically
operated by controller 94 through c.or.nmand fines, 108, 109 and 21Ef,
respectively.
1 o When switching from a heating mode to a cooling mode or vice verse,
the flow control valves are switched accord'r.cigiy. In accordance with one
embodiment af the invemion, the fluid outlet 246 is provided with a beat
sensor 272 wliich allows switc,hing oftbe retuning fluid from one reservoir to
azwther only upon sens'ng an abrnpt tcmpEzature change by ' sensiztg
15 device 272, which then tratsmits a data signal to controller 94 which in
turn,
causes flow control valve i=o mitch. The arrangement is such tha3: the f=
flow control valve to be switched widi be valve 107 and if, for example, the
switch was $xm a cold fluid to a bot fluid, valve 106 will continue to direct
the return fluid into reservoir 9,9 and only upon registering an abrupt
20 temperature drop by sensor device 272 w-ill be return fluid be channeled to
reservoir 96.
In other embodiments, such as that shown in Fig. 8, heating and
cooling of the wozking fluid is carrieci out "Qn-line " by a lieat puuxp
operating
as heater/cooler unit. Such a unit which may, for example, be provided wifih
z5 Peltier effect heat pumps, may easily be con'trolled to either heat or cool
the
fluid passing therethroeigh.
A sob=wfic description of a systern i.n accordance wi#h an
embodiment of the invention can be seea in Fig. S. T3ere a.~~aia, tiIc
rcference
to those used previously in the description, w-iYh a"300 " indcx were used and
AMENDED SHEET
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reader is referred to the previous description for explanation of their
the
function. Controller 394 is provided with a display 311 to display the
registered parameters, e.g. measured core temperature, the measured skin
temperature, the desired core temperature, flow rate, fluid temperature, etc.
In
addition, controller is provided with a control panel 312 and a processor 313.
The processor 313 receives data signals from all sensing devices (core
teinperature measuring device 364, skin temperature measuring device 362,
an optional infrared skin-temperature measuring device 314, and others). In
addition, the processor also receives temperature data from inlet and outlet
fluid teinperature sensing devices 370 and 372 and teinperature registered in
heating/cooling device 315 by means of a sensor 316. Device 315 may for
eaainple be a Peltier effect heat pump, as known per se. In addition, the
controller controls the flow rate of pump 308 via command line 317 and
controls the teinperature of device 315 through line 318.
On the basis of the various data signals registered by the processor, and
implementing various algorithms designed in accordance with the general
teaching of the invention, e.g. that exeinplified below, the flow rate of the
fluid and/or the teinperature of the fluid may be controlled. Various servo
loops may be implemented through processor 313 for proper control of the
various paratneters.
Fig. 8 shows an algorithm, by way of blocked diagram, of the various
computational steps of the algorithm operating in a processor in accordance
with the embodiment of the invention. Contrary to previous figures, the
reference numerals used in this figure have no bearing to previously used
reference numerals.
In a first decision step 410 the system is initiated and integrity is
checked. If the system detects a fault, in any of its components, a systein
shut
down sequence 412 is initiated. In the initiation step, the various
operational
modes are set. These may be automatic, heating only or cooling only modes.
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Other parameters which may be set by the user are minimal and
maximal pennitted temperature of the heat transfer liquid, typically water to
prevent tissue damage as well as discomfort to the patient, particularly when
not under general anesthesia.
In the next two decision making steps 414 and 416, the actual water
teinperature (designated in the figure as "WATER TEMP ") is compared to the
maximally allowed water temperature ("HIGH TEMP") and to the minimal
allowed water temperature ("LOW TEMP"). In case in step 414 the water
temperature is found to be above the HIGH TEMP limit, a cooling
i o sequence 418 is initiated, and in the case the water is found in step 416
to be
too cold, the heating sequence 420 is initiated.
At the next decision step 422, a mode is selected based on the user's
input, between cooling only mode, heating only mode or automatic mode,
designated 424, 426 and 428, respectively.
In the first decision step 430 of the heating mode, the body core
temperature ("CORE TEMP ") is compared to the desired body core
temperature ("SET POI1VT "). Where the body core teinperature is found to be
above the set point, the system is primed to enter to a standby mode 432,
namely the heating function is terminated. During the standby mode, the core
temperature is continuously measured and compared to the set point.
When the core temperature is determined to be below the set point, the
water temperature is compared to the high temperature at 434 and if the water
temperature is below the high temp, the heat mode 420 is initiated. If the
water temperature is found to be above high temp, the system is primed again
to enter into a standby mode 432.
In the first decision making step 440 of the cooling mode 424, the
body core temperature is compared to the set point and if found to be below
the set point, the system is primed into standby mode 432. If the core
temperature is below the set point, the system determines whether
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vasoconstriction of the skin has occurred 442. If there is no
vasoconstriction,
the cooling mode progresses into a next decision making step 444 where the
water temperature is coinpared to the minimal allowed temperature. If water
temperature is less than LOW TEMP then the system is primed to enter into a
s standby mode 432, and if above, the cooling sequence 418 is initiated.
In step 442, if vasoconstriction is found to have occurred (i.e. low heat
conductance between the core and the periphery) notwithstanding the fact that
there is a cooling mode, a heating sequence is initiated. When
vasoconstriction is determined to have ceased, the cooling sequence is
reinstated.
In a first decision making step 450, of the automatic mode 428, the
core temperature is compared to the set point, if found to be below the set
point, the systein enters the heating mode 426. If the core temperature is
found to be below the set point, the sequence proceeds to the next decision
making step 452 and there, if the core temperature is found to be above the
set
point, the cooling sequence 424 is initiated. If the core teinperature is
found to
be below the set point, the system is shifted towards the standby mode.
In the algorithm described above, the only parameter controlled is the
water temperature. It should be appreciated, that in other einbodiments,
parameters such as flow rate of the heat transfer fluid may also be
controlled.
In addition, various other parameters, such as blood temperature, based on
data imported from artificial heart-lung apparatus, may also be factored in
the
system's output.
As will be appreciated, the determination of the occurrence of
vasoconstriction may be based on a variety of parameters, as noted above in
the description, making use of data received from one or more of the above
described sensing devices.
